This invention relates to graphics tablets and more particularly to a graphics tablet capable of resolving the three dimensional coordinates of objects. The widespread availability of digital computers has created a demand for coordinate digitizers, that is, apparatus for supplying the coordinates of points to the data storage element within the computer. Once the coordinates are stored in the computer, suitable software can operate on the stored coordinates to generate graphical displays representing the object whose surface points were measured and stored. Known apparatus particularly adapted for use by hobbyists has been limited to two dimensional digitizers. One known system is disclosed in U.S. Pat. No. 4,334,954. In this apparatus two arms are pivotably interconnected to one another so that a pointer can be moved to generally arbitrary points within the plane of a support. In operation, a sketch, graph or other two-dimensional representation is placed on a support beneath the pointer. As the pointer moves along the graph or sketch, signals from two potentiometers are applied to the input of a computer wherein the signals are stored in digital form. Software can be provided to act on the potentiometer output signals to provide the two dimensional coordinates of points beneath the pointer. This device, therefore, is inherently limited to operations within a plane.
Three dimensional position indicating systems are also known for professional applications. One such apparatus is disclosed in U.S. Pat. No. 3,561,125 to Zeidler. In this apparatus a contacting tip element is supported on a range arm which itself is slidingly supported in a gimbal mechanism. This gimbal mechanism permits rotations about a vertical and a horizontal axis. Thus, by extending and rotating the range arm, points within a working volume can be contacted and signals responsive to the extension and rotation of the arm can be operated on in a digital computer to provide the three dimensional spherical coordinates of the desired point. This apparatus thus requires the measurement of the amount of linear extension of the range arm as well as two rotational measurements.
U.S. Pat. No. 3,944,798 to Eaton discloses apparatus particularly adapted for measuring directions. In this apparatus a grooved head is adapted for closely engaging pipes having arbitrary bends. The head is placed into engagement with the pipe and then moved along the pipe. The groove in the head defines a head working direction and it is this direction which can be stored in a digital computer. The working head is connected to a supporting plane by means of a plurality of arms which are pivotably connected to one another. The relative angle between pairs of arms is measured by means of electrical resolvers. This apparatus is bulky and expensive and designed for use with professional manufacturing, assembly and inspection operations. Furthermore, this apparatus employs resolvers for measuring angles.
It is an object of this invention, therefore, to provide a three dimensional graphics tablet or coordinate resolving apparatus which utilizes potentiometers to measure relative angles between link elements for coordinate determinations.
It is a further object of this invention to provide a three dimensional graphics tablet which is of relatively simple mechanical construction and inexpensive to manufacture.
A still further object of this invention is a three dimensional graphics tablet which is highly accurate and very reliable in operation.
Yet another object of this invention is a portable three dimensional graphics tablet which can be clamped to an existing surface such as a desk or table.
These and other objects and advantages of the present invention will become apparent by reference to the reminder of this specification.